This invention relates to apparatus for verifying the authenticity of documents, and more particularly to such verification apparatus for detecting a metallized security thread embedded in currency or banknote paper and for determining its authenticity by detecting the currency paper's denomination indicated by coded metallic patterns disposed on a surface of the security thread.
It is known in the art of currency and banknote papers to incorporate or embed a security thread partially or fully within the paper. The use of such security threads has increased due to the increasing prevalence of high-resolution scanners and true-color photocopying machines and printers--the tools of modern counterfeiters. If modern currency or banknote papers do not have an embedded security thread, the currency can be more easily duplicated with a color photocopier. However, if the security thread is embedded within the paper, the characteristics of the thread are harder to illicitly reproduce.
It is known in the art that the thread may comprise a plastic film or substrate having selected aluminum characters formed on one or both surfaces of the substrate. The thread is typically embedded entirely within the currency paper and is not present on either surface of the paper. Such security threads for use in U.S. currency are described in greater detail in U.S. Pat. Nos. 4,652,015 and 4,761,205. The security thread has printed characters of extreme fine-line clarity and high opacity such that human-readability of the printing is possible by means of transmitted light. Yet, the printing remains completely indiscernible to the human eye under reflected light. Further, the highly reflective metallic coating causes the thread to virtually disappear under the reflected light used by modern photocopier equipment. If the printing were legible under reflected light, the public could rely upon the presence of the printed matter solely by visual inspection. The printing would then be easily replicated by counterfeit means.
The aforementioned patents ensure that the public does not come to rely on such an easily simulated security thread characteristic. This is accomplished by a method of manufacturing currency and banknote papers containing a security thread that is virtually invisible under reflected light with no manifestation on the surface of the currency or banknote paper that such a security thread is present within the note. Thus, authentication of such a security thread is carried out in a two-fold test; namely, wherein the thread is legible under transmitted light and invisible under reflected light.
An easy way of checking the authenticity of such a security thread is to place the currency under an intense light source to observe the thread characters by the human eye. Although visual inspection can generally detect the counterfeit notes (given the proper lighting conditions), visual inspection is slow, time consuming and expensive. Further, in commercial situations where such an intense light source is unavailable (thus making a human check for thread presence and authenticity virtually impossible), it is desirable to provide means for automatically determining the thread's presence and authenticity. Various means for verifying the presence and authenticity of the aforementioned security thread are exemplified in U.S. Pat. Nos. 4,980,569 and 5,151,607.
The '569 patent discloses a verification device comprising two optical light source/detector pairs disposed on opposite sides of a currency paper. The source and detector pairs are arranged for transmission and reception of optical energy through the currency if the thread is not present. Also, the source and detector pairs can determine the presence of a counterfeit thread on the currency surface by checking for light reflected off of the currency surface. Thus, the '569 patent provides a two-fold test wherein the thread, to be genuine, must be detected under transmitted light, and not be detected under reflected light. However, the device in the '569 patent may give a false indication of the authenticity of a counterfeit currency when a pencil line is drawn on the currency surface at the normal thread location.
In an attempt to overcome the shortcomings of the '569 patent, the '607 patent discloses a verification device comprising the optical means of the '569 patent in combination with a magnetic detector. The magnetic detector determines the presence of the security thread, while the optical means determines whether the thread is properly within the currency or improperly disposed on either surface.
In light of the shortcomings of optical methods of verifying the presence of the security thread within the currency paper, other verification means have been developed, such as capacitive devices. These devices operate on the principle of detecting a change in capacitance of a sensor, such change being due to the dielectric properties of the metallized security thread. The metallized thread has dielectric properties that are vastly different from those of the paper. The security thread operates as one plate of a capacitor, and draws charge off of a second plate of the capacitor, the second plate typically being a sensing part of the verification device. In contrast, the paper itself has little or no effect on the amount of charge on the sensing plate. Thus, the security thread effectively increases a capacitance value that is sensed by the verification device, a detectable feature.
However, capacitance verification devices have shortcomings in that they can also be fooled by conductive marks, such as pencil lines, placed on the surface of the currency. This can be especially problematic for currency verification devices used for unattended transactions; for example, in vending machines that incorporate currency acceptors. Automatic vending machines, such as those that dispense soft drinks and cigarettes, are gradually accepting higher denomination currency bills in unattended transactions as payment. This is due, in part, to the inflationary prices of goods. Also, unattended bill acceptors are expanding into areas such as gaming and other entertainment vending areas, and gas stations. The addition of bill acceptors and/or changers in these vending machines has resulted in a large increase in sales for unattended transactions. For these types of machines, it is imperative that the bill acceptor/changer have some means for reliably discriminating between genuine and counterfeit bills. Examples of security thread verification devices that provide for machine readability of a metallized security thread using a capacitance bridge technique are disclosed in U.S. Pat. Nos. 5,308,992 and 5,394,969.
The aforementioned security thread may have its printed characters formed on the plastic substrate either in the form of positive image metal characters or partially demetallized threads that display negative image or clear characters. In other words, the positive image thread has metal characters formed on the plastic substrate. The metal only occupies the areas on the thread defined by the characters. Such positive image threads are used in United States currency paper. On the other hand, the negative image thread has its characters formed by the removal of metal at the desired character locations. The non-character portion of the thread surface is coated with metal. Therefore, the non-metal or "clear text" characters are defined by metal boundaries. Such negative image security threads are used in currencies such as the German Deutsche Mark.
In contrast to the two types of security threads described hereinabove having selected metallized characters formed thereon, it is known in the art to use a "solid" security thread. Such a thread comprises a plastic substrate having metal (e.g., aluminum) deposited entirely on one or both surfaces of the plastic substrate. Such "solid" or "continuously metallized" threads sometimes have indicia printed thereon indicative of, e.g., currency denomination. However, normally the printing cannot be seen even under an intense light source; therefore, such printing is oftentimes eliminated. It is known to use such "solid" security threads within the currency of, e.g., Saudi Arabia.
The aforementioned three types of security threads may all be visually detected by the human eye by first holding the currency paper up to relatively strong transmitted light and then verifying the presence of the thread within the paper. Also, these threads may also be automatically or machine detected by various means, including the aforementioned capacitive detection schemes. However, all such schemes merely determine only the presence or absence of the three types of thread within the paper. The authenticity of the paper then depends only upon the presence or absence of the thread within the paper. With such threads, there typically is no known method of determining a distinguishing feature of the paper, such as its denomination, using capacitive techniques. This is due primarily to the small size of the characters formed on the thread. Instead, optical character recognition or other imaging-based schemes would have to be employed to ascertain such relatively detailed information, such as denomination, as indicated by the printed text used by the aforementioned security threads.
In the alternative, the aforementioned threads or other types of threads may be coated with a layer of magnetic material, and also with either a luminescent, an x-ray absorbent, or a non-magnetic metal material. The magnetic material may be applied in a coding pattern (e.g., magnetic coating applied discontinuously onto a thread with the discontinuities detected with a field-detecting device, or two different magnetic materials provided in alternating bands along the thread), as described in U.S. Pat. No. 4,183,989. However, such feature, although machine readable, does not offer a public security feature, such as printed text, that is visual under transmitted light. Moreover, relying upon the field produced by a certain magnitude or configuration of magnetic materials is problematic in that such coded variations are subject to obliteration by intentional or accidental demagnetization subsequent to the original magnetization.
In addition, although magnetic metal, such as iron oxide coatings, can be applied discontinuously onto a thread in a bar code-like sequence or in varying depths of coating, to accomplish a machine-readable feature, such application processes require specialty screen printing equipment to apply the iron oxide slurry in defined bars. Moreover, magnetic field array detectors are required to resolve the coded sequence. These array detectors are expensive to manufacture and are particularly problematic for reading threads when banknotes or other documents are processed narrow-edge versus wide-edge, where the number of sites on the array that are processed for the wide-edge feed condition are reduced.
Therefore, in response to the difficulty of obtaining a relatively simplified method of providing a security thread having easily-implementable features indicative of denomination, a security thread may be provided comprising a plastic substrate having a sequence of coded metallic patterns deposited on one or both substrate surfaces in a repeating pattern. Such repeating pattern provides a first type of security detection feature. A second type of security detection feature is provided by metallic indicia, either in the form of positive- or negative-image characters formed at various locations within the repeating metallic patterns. This second security feature allows for manual visual verification by the human eye of both the thread and its denomination under relatively strong transmitted light.
Accordingly, it is a primary object of the present invention to provide a device that verifies both the authenticity and denomination of a currency paper.
It is a general object of the present invention to provide a device that verifies both the authenticity and denomination of a currency paper by detecting a security thread embedded within the paper.
It is a further object of the present invention to provide a device that verifies both the authenticity and denomination of a currency paper having a rectangular-shaped security thread embedded therein, wherein the security thread is normally embedded in the paper in a direction parallel to the narrow edge of the paper, the device being able to detect the thread as the device is passed over the thread either parallel to the long dimension of the thread (i.e., in the wide-edge direction), or perpendicular to the long dimension of the thread (i.e., in the narrow-edge direction).
It is still another object of the present invention to provide a device that rapidly senses and counts the number of electrically-conductive patterns on a security thread embedded within currency paper or the like in order to both authenticate the currency paper and determine its denomination.
It is yet another object of the present invention to provide for high-speed, automated document verification.
It is still another object of the present invention to provide for cost-effective counterfeit deterrence in security documents such as currency paper.
It is another object of the present invention to provide for a currency paper authentication and denomination determining device that can be easily and cost effectively incorporated into known or future automated processing equipment, such as high-speed central bank sorting machines, low-cost table-top currency counters found in local bank branches or businesses, and bill acceptors and/or changers embodied in vending machines.
It is yet still another object of the present invention to provide for accurate low-cost, high-speed commercial sorting of currency paper.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.